In general, a driver of a vehicle may perform a downshift operation in front of a corner for the purpose of, for example, deceleration of the vehicle, stabilization of the vehicle behavior, or immediate generation of driving force at a rising of the corner. By performing the downshift operation in front of the corner, an engine braking is effectively usable to achieve the deceleration of the vehicle, the stabilization of the vehicle behavior, or the like.
When the downshift operation is performed by a manual operation in an automatic transmission, the driver performs the downshift by selecting a speed change stage one by one through, for example, a shift lever operation in a manual range, or an operation of a paddle switch disposed on a steering wheel. However, multi-staging of recent automatic transmissions is remarkable, and it is therefore necessary to perform the downshift operation several times until obtaining an intended engine braking amount. This can be time consuming. For example, during traveling at a high speed stage, such as on high speed traveling, the high speed stage has a high ratio and there is a small ratio difference between a plurality of speed change stages. Hence, it particularly takes time to achieve the downshift from the high speed stage to an intended speed change stage.
Meanwhile, as one of automatic downshift control in a conventionally known automatic transmission, for example, the following Patent document 1 discloses detecting a corner ahead of a vehicle and determining a speed change stage that becomes a target of downshift, taking the corner ahead into consideration. However, downshift control that fits characteristics of the corner is insufficient only by detecting the corner and performing downshift control accordingly as in the case with this conventional technology. In particular, a blind corner where an end of the corner is not visible needs more attention during traveling, for example, because it is necessary to consider a situation where an obstacle, such as a vehicle and a falling object, may suddenly appears at the end of the blind corner. This necessitates a larger deceleration than the case of passing through a highly-visible corner, and there remains a desire for downshift control that fits the characteristics of the corner.
For example, Patent document 2 discloses as follows. When a vehicle enters a corner, a determination is made as to whether the corner is a blind corner where the front is not visible from a viewpoint of a driver. In the case of the blind corner, it is configured to generate an alarm or control a traveling state of the vehicle. However, Patent document 2 merely describes determining a downshift amount according to a vehicle speed as one of control of the traveling state of the vehicle at the blind corner (refer to paragraph [0214] etc. in Patent document 2). This disclosure does not also consider performing the downshift control that fits the characteristics of the blind corner.